System and method for rapid examination of vasculature and particulate flow using laser speckle contrast imaging

ABSTRACT

Examination of the structure and function of blood vessels is an important means of monitoring the health of a subject. Such examination can be important for disease diagnoses, monitoring specific physiologies over the short- or long-term, and scientific research. This disclosure describes technology and various embodiments of a system and method for imaging blood vessels and the intra-vessel blood flow, using at least laser speckle contrast imaging, with high speed so as to provide a rapid estimate of vessel-related or blood flow-related parameters.

RELATED APPLICATIONS

This application is a National Stage application under 35 U.S.C. 371 ofPCT International Application No. PCT/US2016/055976, filed Oct. 7, 2016,which claims the benefit of U.S. Provisional Application No. 62/239,529,filed Oct. 9, 2015 the entire disclosure of which is hereby incorporatedby reference herein.

GOVERNMENT GRANT SUPPORT

This invention was made with government support under grant1R43EB019856-01A1 awarded by the National Institute of BiomedicalImaging and Bioengineering (of the National Institutes of Health). Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates generally to vascular imaging technologiesand methods and, more particularly, to the rapid examination ofvasculature and blood flow using laser speckle contrast imaging.

BACKGROUND

Blood vessels are the fundamental mechanism by which human and animalbiological systems and related tissues, organs, and organ systemsreceive nutrient supply and remove waste products to maintain itsviability, integrity, and functionality. Anatomical characteristics ofblood vessels (e.g., size, structure, orientation, location, quantity,distribution, and type) are specific to each biological system, tissue,organ, or organ system. Many pathologies manifest as changes in theseanatomical characteristics and are also accompanied by changes invascular physiology (e.g., velocity or flow rates of blood within anindividual vessel, group of vessels, or network of vessels; distributionof blood flow within a group or network of connected or independentvessels, including regions of vascular profusion and non-perfusion; andvessel compliance, contractility, and proliferation). For example,diabetic retinopathy (DR) is a vision-threatening complication ofdiabetes that manifests as progressive narrowing of arteriolar caliberuntil occlusion occurs. Vessel occlusion is typically followed by vesselproliferation (i.e., angiogenesis), which results in increased visionloss and progression toward blindness. Numerous other diseases andconditions involve pathologies or symptoms that manifest in blood vesselanatomy or physiology. Diseases associated with modified or abnormalvasculature in the eye include DR, hypertensive retinopathy (HR),glaucoma, age-related macular degeneration (AMD), retinopathy ofprematurity (ROP), and choroidal neovascularization (CNV), among others.Vascular changes in the eye are also associated with systemic diseases,including sleep apnea. Alzheimer's disease, brain lesions (e.g.,stroke), various complications of cardiovascular disease, and metabolicdiseases (e.g., diabetes and hyperthvroidism). Various dermatologicaldiseases and conditions, including melanoma, diabetic foot ulcers, skinlesions, wounds, and burns, involve injury to or pathophysiology of thevasculature.

These anatomical and physiological characteristics are important for thedevelopment of novel diagnostics and therapeutics; the diagnosis,management, and treatment of many diseases and medical conditions; andthe advancement of standard of care for patients (human and animal). Byevaluating the anatomical and physiological characteristics of thevasculature (directly or indirectly, quantitatively or qualitatively), ascientist, clinician, or veterinarian can begin to understand theviability, integrity, and functionality of the biological system,tissue, organ, or organ system being studied. Depending on the specificcondition being studied, important markers may manifest as acute orlong-term alterations in blood flow or other anatomical andphysiological characteristics of the vasculature. For example,anatomical and physiological information, in either absolute terms or asrelative changes, may be used as a mechanism for monitoring andassessing changes in the retinal vasculature to determine the risk ofblindness associated with DR, the likely onset of visual impairment, andpotential disease management and treatment options, among other things.Likewise, almost all types of tumors are accompanied by vascular changesto the cancerous tissue; tumor angiogenesis and increased blood flow isoften observed in cancerous tissue due to increased metabolic demand ofthe tumor cells. Similar vascular changes are associated with healing ofinjuries, including wounds and burns, where angiogenesis serves acritical role in the healing process. Hence, anatomical andphysiological information may assist a clinician or veterinarian in themonitoring and assessment of healing after a severe burn, recovery of anincision site, or the effect of a therapeutic agent or other type oftherapy (e.g., skin graft or negative pressure therapy) in the treatmentof a wound or diabetic foot ulcer.

Monitoring and assessment of anatomical and physiological informationcan be critically important for surgical procedures. The imaging ofblood vessels, for example, can serve as a basis for establishinglandmarks during surgery. During brain surgery, when a craniotomy isperformed, the brain often moves within the intracranial cavity due tothe release of intracranial pressure, making it difficult for surgeonsto use preoperatively obtained images of the brain for anatomicallandmarks. In such situations, anatomical and physiological informationmay be used by the surgeon as vascular markers for orientation andnavigation purposes. Anatomical and physiological information alsoprovides a surgeon with a preoperative, intraoperative, andpostoperative mechanism for monitoring and assessment of the targettissue, organ, or an individual blood vessel within the surgical field.

The ability to quantify, visualize, and assess anatomical andphysiological information in real-time or near-real-time can provide asurgeon with feedback to support diagnosis, treatment, and diseasemanagement decisions. An example of a case where real-time feedbackregarding anatomical and physiological information is important is thatof intraoperative monitoring during neurosurgery, or more specifically,cerebrovascular surgery. The availability of real-time blood flowassessment in the operating room (OR) allows the operating neurosurgeonto guide surgical procedures and receive immediate feedback on theeffect of the specific intervention performed. In cerebrovascularneurosurgery, real-time blood flow assessment can be useful duringaneurysm surgery to assess decreased perfusion in the feeder vessels aswell as other proximal and distal vessels throughout the surgicalprocedure.

Likewise, rapid examination of vascular anatomy and physiology hassignificant utility in other clinical, veterinary, and researchenvironments. For example, blood flow is often commensurate with thelevel of activity of a tissue and related organ or organ system. Hence,vascular imaging techniques that can provide rapid assessment of bloodflow can be used for functional mapping of a tissue, organ, or organsystem to, for example, evaluate a specific disease, activity, stimulus,or therapy in a clinical, veterinary, or research setting. Toillustrate, when the somatosensory region of the brain is more activebecause of a stimulus to the hand, the blood flow to the somatosensorycortex increases and, at the micro-scale, the blood flow in the regionof the most active neurons increases commensurately. As such, ascientist or clinician may employ one or more vascular imagingtechniques to evaluate the physiological changes in the somatosensorycortex associated with the stimulus to the hand.

A number of vascular imaging approaches exist to evaluate anatomical andphysiological information of the tissue vasculature. Magnetic resonanceimaging (MRI), x-ray or computerized tomography (CT), ultrasonography,laser speckle contrast imaging (LSCI), and positron emission tomography(PET) are among a number of imaging techniques that offer quantitativeand qualitative information about the vascular anatomy and physiology.Each technique offers unique features that may be more relevant to theevaluation of a particular biological system, tissue, organ, or organsystem or a specific disease or medical condition.

LSCI has particular relevance in the rapid, intraoperative examinationof vascular anatomy and physiology. LSCI is an optical imaging techniquethat uses interference patterns (called speckles), which are formed whena camera captures photographs of a rough surface illuminated withcoherent light (e.g., a laser), to estimate and map flow of variousparticulates in different types of enclosed tubes. If the rough surfacecomprises moving particles, then the speckles corresponding to themoving particles cause a blurring effect during the exposure time overwhich the photograph is acquired. The blurring can be mathematicallyquantified through the estimation of a quantity called laser specklecontrast (K), which is defined as the ratio of standard deviation tomean of pixel intensities in a given neighborhood of pixels. Theneighborhood of pixels may be adjacent in the spatial (i.e., within thesame photograph) or temporal (i.e., across sequentially acquiredphotographs) domains or a combination thereof. In the context ofvascular imaging, LSCI quantifies the blurring of speckles caused bymoving blood cells within the blood vessels of the illuminated region ofinterest (ROI) and can be used to analyze detailed anatomicalinformation (which includes but is not limited to vessel diameter,vessel tortuosity, vessel density in the ROI or sub-region of the ROI,depth of a vessel in the tissue, length of a vessel, and type of bloodvessel, e.g., its classification as artery or vein) and physiologicalinformation (which includes but is not limited to one or more of bloodflow and changes thereof in the ROI or a sub-region of the ROI, bloodflow in an individual blood vessel or group of individual blood vessels,and fractional distribution of blood flow in a network of connected ordisconnected blood vessels).

While non-LSCI methods of intraoperative real-time blood flow assessmentare currently used, no single method is considered adequate in allscenarios. For example, in the context of cerebrovascular surgery suchas aneurysm surgery, imaging of small yet important vessels calledperforators necessitates a high-resolution imaging technique formonitoring anatomical and physiological information, which is currentlyunavailable in the neurosurgical OR. The use of Indocyanine Green (ICG)Videoangiography has been assessed for this purpose but challenges stillremain because of the potential for dye leakage. Intraoperativeangiography is currently considered the gold standard to assess vesselpatency following a number of cerebrovascular procedures (e.g., aneurysmclipping and arteriovenous malformation. AVM, obliteration). However,angiography does not provide real-time assessment during the actualperformance of surgery. Furthermore, given the invasive nature of thistechnique, and despite advancements, the risk of complications is noteliminated. In AVM surgery, real-time blood flow assessment helps thesurgeon better understand whether particular feeding vessels carry highflow or low flow, which could ultimately impact the manner in whichthose vessels are disconnected from the AVM (i.e., bipolar cauteryversus clip ligation). Finally in a disease such as Moyamoya, which mayrequire direct vascular bypass, real-time flow assessment can be usefulin identifying the preferred recipient vessels for the bypass as well asassessing the flow in that bypass and surrounding cortex once theanastomosis is completed.

The real-time assessment of blood flow may be helpful in other surgeryfields that rely on vascular anastomoses as well, specifically plasticsurgery, vascular surgery, and cardiothoracic surgery. Currently,technology such as the use of Doppler ultrasonography is used to confirmthe patency of an anastomosis. However, real-time, quantitative imagingcan add a tremendous benefit in assessing the adequacy of a bypass,revealing problems to the surgeon in real time to facilitate correctionduring surgery rather than postoperatively when either it is too late orthe patient requires a reoperation.

LSCI has been used as a blood flow monitoring technique in the OR. LSCIhas been considered for functional mapping in awake craniotomies toprevent damage to eloquent regions of the brain, to assess the surgicalshunting of the superior temporal artery (STA) and the middle cerebralartery (MCA) and for intraoperative monitoring during neurosurgery.These approaches have limitations of spatio-temporal resolution andavailability of anatomical and physiological information on a real-timeor near-real-time basis.

SUMMARY OF THE INVENTION

This disclosure relates to technology and various embodiments of asystem for rapid examination (i.e., real-time or near-real-time) ofvasculature and particulate flow using LSCI. In various embodiments, thesystem comprises at least one illumination module and at least one lightmanipulation component to illuminate the ROI of a target tissue, atleast one camera module and at least one optical element for capturinglight reflected from the ROT of a target tissue, at least one processorthat is programmed to calculate, estimate, and/or determine anatomicaland physiological information in real-time or near-real-time using atleast LSCI, at least one storage module for short- and long-term accessor archival of electronic data captured, acquired and/or generated bythe system, and at least one display module that presents the anatomicaland physiological information in real-time or near-real-time.

In various embodiments, the at least one light source comprises at leastone coherent light. In some embodiments, the at least one light sourcecomprises at least one coherent light and one or more non-coherent orpartially coherent light. In various embodiments, the at least one lightmanipulation component comprises lenses, mirrors, apertures, filters,beam splitters, beam shapers, polarizers, wave retarders, and fiberoptics. In various embodiments, the target tissue comprises the cornea,sclera, retina, epidermis, dermis, hypodermis, skeletal muscle, smoothmuscle, cardiac muscle, cerebrovascular tissue, the stomach, large andsmall intestines, pancreas, liver, gallbladder, kidneys, and lymphatictissue. In various embodiments, the target tissue is in situ, in vivo,or in vitro. In various embodiments, the at least one camera modulecomprises a charge coupled device (CCD), complementary metal oxidesemiconductor (CMOS), metal oxide semiconductor (MOS), or photo-tubes.In various embodiments, the at least one optical element compriseslenses, mirrors, apertures, filters, beam splitters, beam shapers,polarizers, wave retarders, and fiber optics. In various embodiments,the at least one processor comprises a field programmable gate array(FPGA); the central processing unit of a personal computer, laptopcomputer, mobile computing platform, remote server or server system; anoff-the-shelf microprocessor; or equivalent computing device. The atleast one processor may also comprise a graphics processing unit (GPU),a specialized processor configured for handling graphical and imagedata. The processor may operate a single or multiple cores and carry outserial or parallel computations. In various embodiments, the anatomicalinformation includes, but is not limited to, size (e.g., diameter andlength), structure (e.g., thickness and tortuosity), orientation (e.g.,depth in the tissue, relative relation to other anatomical featureswithin the ROI), location (e.g., relative relation to other anatomicalfeatures within the organ, organ system, or biological system),quantity, distribution (e.g., density in the ROI or sub-region of theROI), and type of blood vessels (e.g., artery, arteriole, vein, venule,or other classification). In various embodiments, the physiologicalinformation includes, but is not limited to, velocity or flow rates ofblood within an individual vessel, group of vessels, or network ofvessels; distribution of blood flow within a group or network ofconnected or independent vessels, including regions of vascularprofusion and non-perfusion; and vessel compliance, contractility, andproliferation. In various embodiments, the calculating, estimating, anddetermining in real-time comprises performing a processing step within40 milliseconds of the original event that triggered the processingstep. In various embodiments, the calculating, estimating, anddetermining in near-real-time comprises performing a processing stepbetween 40 milliseconds and 1000 milliseconds of the original event thattriggered the processing step. In various embodiments, generating anLSCI image comprises at least the calculation of laser speckle contrastvalues at one or more pixels of interest by utilizing the intensities ofpixels in a spatial, temporal, or spatio-temporal neighborhood aroundthe one or more pixels of interest; and may also comprise estimation ofspeckle contrast-derived secondary values that can be utilized inestimation of anatomical and physiological information local to thefeature at the one or more pixels of interest. In various embodiments,the at least one storage device comprises random access memory (RAM)units, flash-based memory units, magnetic disks, optical media, flashdisks, memory cards, or external server or system of servers (e.g., acloud-based system) that may be accessed through wired or wirelessmeans. In various embodiments, the electronic data comprises raw imagedata captured by the at least one camera sensor, anatomical andphysiological information or equivalent parameters calculated from theraw or processed image data, patient-specific data manually entered orautomatically acquired from another source (e.g., electronic healthrecord, electronic medical record, personal health record, picturearchiving and communications system, PACS, or other sensors, includingheart rate monitor, finger plethysmograph, respirator, or othersurgical, anesthesiological, or medical equipment), derivative dataassociated with the processing of these electronic data, or control andguidance information (e.g., scale bars, menu options, operatinginstructions, error messages) or a combination thereof. In variousembodiments, the at least one display device comprises a digital oranalog 2-dimensional or 3-dimensional presentation system (e.g.,television, computer monitor, head-mounted display, or mobile computingplatform screen) based on various technologies (e.g., cathode ray tubes,light-emitting diodes, plasma display technology, liquid crystalsdisplay technology, or carbon nanotubes). In some embodiments, the atleast one display device presents electronic data, including theanatomical and physiological information or equivalent parameterscalculated from the raw or processed image data, in a manner that allowsan observer to visualize the information, parameters, or electronic dataoverlaid on the FOV of the target tissue. In some embodiments, thesystem is designed to present electronic data, including the anatomicaland physiological information or equivalent parameters calculated fromthe raw or processed image data, to the user via the viewing lens of thesystem, an associated microscope, or other surgical instrument.

This invention further relates to technology and methods for rapidexamination of vasculature and particulate flow using LSCI. To produceLSCI data, a stack of N image frames is captured under coherentillumination and speckle contrast K(P₀) is calculated at every pixel ofinterest P₀ using Eq. 1.

$\begin{matrix}{{K( P_{0} )} = {\sigma_{{\mathbb{N}}{(P_{0})}}\text{/}\mu_{{\mathbb{N}}{(P_{0})}}}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$where σ

_((P) ₀ ₎ and μ

_((P) ₀ ₎ are the standard deviation and mean, respectively, in theintensity of all pixels on a defined local neighborhood

(P₀). K(P₀) values can be calculated such that

(P₀) is chosen exclusively in either the spatial domain called sLSCI(Eq. 2a) or the temporal domain called tLSCI (Eq. 2b).

(P ₀)={P(x,y,n ₀)s·t·∥(x,y,n ₀)−(x ₀ ,y ₀ ,n ₀)∥≤4 px}  Eq. 2a

(P ₀)={P(x ₀ ,y ₀ ,n)s·t·|n−n ₀|≤80 frames}  Eq. 2b

In the above equations, x- and y-coordinates represent spatialcoordinates, while n represents the temporal placement of the pixel bydenoting the frame number in which the pixel is located. Thus, pixel P₀is appropriately represented by the coordinates (x₀, y₀, n₀).

Blood velocity is known to be proportional to a parameter l/τ_(c) (whereτ_(c)(P₀) is the correlation time of intensity fluctuations) that can becomputed from K(P₀) using Eq. 3.

$\begin{matrix}{\lbrack {K( P_{0} )} \rbrack^{2} = {\frac{\tau_{c}( P_{0} )}{T}\{ {2 - {\frac{\tau_{c}( P_{0} )}{T}\lbrack {1 - {\exp( {- \frac{2T}{\tau_{c}( P_{0} )}} )}} \rbrack}} \}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

Thus, plots of l/τ_(c) and a plot of K(P₀) are each indicative of bloodvelocity and flow and potential constituents of anatomical andphysiological information. Both these plots can be displayed ingrayscale or pseudo-color for visualization purposes.

Spatial processing of speckle data requires only N=1 image frame beacquired and preserves temporal resolution for sequential monitoring,but suffers from a compromised spatial resolution. The degree ofcompromise in spatial resolution depends on the number of pixels in thespatial neighborhood chosen for calculation of speckle contrast.

For high-resolution LSCI, speckle contrast is calculated using atemporal algorithm that requires the processing of a time-stack ofseveral (typically N=80, but may be different) images. This reduces thetemporal resolution of any functional information extracted from thedata, and also the prolonged image acquisition time makes the system andmethod susceptible to motion artifact. Even if images were acquired at150 frames per second (fps), generating an LSCI image from the 80 frameswould require over 0.5 s. To avoid the slow output rate, specklecontrast can be calculated over a rolling time-stack of images—that isby including each new image frame to the processing image stack andremoving the oldest image from the stack. This first in first out (FIFO)strategy coupled with fast implementation of speckle contrastcalculations allows the output rate to be as high as the camera framerate but the system would still suffer from latency (i.e., the outputwould trail the real-time event by a latency of at least the amount oftime that is required to acquire the N=80 image frames). If theacquisition speed is 150 fps, the latency corresponding to theacquisition of 80 frames, would be 0.533 seconds.

To counter this problem and achieve rapid examination of vasculature andparticulate flow, the subject invention includes a method of calculatingspeckle contrast using a combination of spatial processing and temporalprocessing schemes. A pixel-neighborhood that is cuboidal in thespatio-temporal domain is used for calculating speckle contrast. Forexample, a pixel-neighborhood of 5 pixels×5 pixels×5 frames around it isextracted for every pixel P₀ (see Eq. 2) for contrast calculation, asexpressed in Eq. 4.

(P ₀)={P(x,y,n)s·t·∥(x,y)−(x ₀ ,y ₀)∥≤2 px and |n−n ₀|≤2frames}  Eq. 4K(P₀) is then calculated using Eq. 1. We have previously demonstrated afield programmable gate array (FPGA) based hardware implementation oftemporal contrast calculations. Similar FPGA-based hardwareimplementations for spatial contrast calculations have also beenreported, stLSCI strikes a balance between spatial and temporalresolution while still utilizing adequate number of pixels for robustspeckle contrast calculation. The neighborhood in the spatial domain andnumber of frames used in processing in the temporal domain may be chosenin accordance with the requirements of the imaging application, stLSCIperforms on par with sLSCI and tLSCI in reproducibility of specklecontrast values and the ability to discriminate vessels from backgroundtissue. The choice of number of pixels in the spatio-temporalneighborhood may be as few or as many depending on the desiredspatio-temporal resolution in the output of imaging and the spatialresolution and frame rate of image acquisition. So, when using a cameraoperating at 120 Hz, it would be possible to use twice as many framesfor stLSCI calculations without compromising the temporal resolution ofthe output as one would when using a camera operating at 60 Hz.Similarly, choice of the number of pixels in each frame that constitutethe spatio-temporal neighborhood would also depend on the spatialresolution at which image acquisition is performed.

Once plots of l/τ_(c) or K are obtained, these plots may be processedfurther to obtain anatomical and physiological information, including:

-   -   Blood velocity—Blood velocity may be estimated as a linear or        polynomial function of l/τ_(c) values at the location.        Subsequently, blood perfusion in a region of the ROI may be        estimated using these blood velocity estimates.    -   Vessel diameter—Vessel diameters may be estimated using the        appearance of the K or l/τ_(c) values within the vessel with        respect to those outside the vessel. Comparison of appearance        includes comparison of not only the intensities but also the        gradient of intensities as well as other features such as        ridge-like appearance of vessels or the connectedness of vessels        with other vessels. Ridge-like appearance can be formulated        using the Hessian matrix and its eigenvalues computed for the        LSCI image of the ROI.    -   Vascular blood flow—Blood flow within blood vessels may be        estimated by combining both values of l/τ_(c) and value(s) of        vessel diameter. In one method, vascular flow may be obtained by        integrating the values of blood velocity along the cross-section        of the vessel. In another method, vascular flow may be estimated        by multiplying the average blood velocity with the diameter of        the vessel. Curve fitting may be used to refine the estimates of        blood velocity or vessel diameters.    -   Depth of the vessel in the tissue—Depth of the blood vessel may        be estimated using LSCI at multiple different wavelengths, which        penetrate the tissue to different extents, thus resolving the        vessel based on the appearance of the vessel in the LSCI image        obtained at each wavelength relative to its appearance in LSCI        images obtained at other wavelengths.    -   Length of the vessel—Length of the vessel may be estimated by        tracking the blood vessel or its centerline at a pixel level        from one point to another. The sum of pixel-to-pixel distances        may be reported as is, or the pixel-to-pixel distances may be        refined to obtain a smooth traversal prior to estimating the        total length.    -   Vessel Tortuosity—Tortuosity of the vessel may be estimated        utilizing one of the following methods. One method includes        estimation of tortuosity between two locations on any vessel of        interest as the ratio of the length of the vessel along its axis        between the two locations to the straight line distance between        the two locations. Another method includes estimation of        tortuosity between two locations on any vessel of interest as        the number of times the curvature of the vessel changes per unit        length of the vessel while axially traversing the vessel between        the said two locations on the vessel.    -   Type of blood vessel—An artery (or an arteriole) may be        discriminated from a vein (or a venule) by analyzing the        vessel's appearance in the LSCI image and a colored or        monochrome photograph (reflectance or absorption image in        non-coherent light). Arterial vessels have higher blood        velocities as compared to venous vessels, and also carry more        oxygenated blood, which has different light absorption        properties.

The subject invention can be embodied differently for differentapplications that include acute or longitudinal clinical diagnostic andmonitoring purposes, clinical decision support, and research uses. Invarious embodiments, the invention is utilized in a manner such that thetarget is any enclosed tube (i.e., analogous to blood vessels) andparticulate flow (i.e., analogous to blood flow). An example of such atarget may be a plastic tube with artificial blood flowing through it,or microfluidic channels with microbeads flowing through them. Thelymphatic system is another example of a target that the subjectinvention may be utilized for imaging.

In various embodiments, the system and method are designed for real-timeor near-real-time blood flow imaging during surgery, includingcerebrovascular surgery and other neurosurgeries; plastic andreconstructive surgery; ophthalmic surgery; cardiac surgery; endoscopicsurgery; ear, nose, and throat (ENT) surgery; and dental surgery. Ineach case, such assessment of one or more electronic data may lead toactionable outputs such as surgical planning, diagnosis of intended orincidental conditions or complications, prognosis of the outcome of thesurgery, modifying the course of the surgery in real-time, short orlong-term treatments or therapies, or management of health post-surgery.The actionable output may result from considering the assessment of theone or more electronic data in conjunction with information gatheredfrom other sensory or therapeutic medical device equipment or diseasemanagement system.

Cerebrovascular Surgery and Other Neurosurgeries:

In preparation for cerebrovascular surgery, the surgical teamestablishes a surgical plan, typically based on MRI and CT images of thepatient's brain. The surgical plan involves a strategy for navigating tothe specific surgical site in a way that minimizes risk of damage to thevascular anatomy. The surgical procedure often requires the use of anoperating microscope to observe the surgical field and typicallyinvolves observation of vessel patency and vessel-specific physiologicalinformation in the surgical field. In an aneurysm surgery, for example,blood flow in perforator vessels associated with the aneurysm and itsparent vessels are of great importance for clinical outcomes and, hence,an important monitoring target. Other types of neurosurgeries for whichobservation of vessel patency and vessel-specific anatomical andphysiological information in the surgical field is important includevascular grafting surgeries in patients suffering from Moyamoya disease,arteriovenous malformation surgeries, brain tumor resection surgeries,awake craniotomies where functional mapping is desired, spinal cordsurgeries, and surgeries performed to relieve carpel tunnel syndrome.The subject invention can be embodied to provide the surgeon withreal-time or near-real-time assessment of vessel patency andvessel-specific anatomical and physiological information to improve theefficiency and effectiveness of cerebrovascular and other neurosurgicalprocedures.

Plastic and Reconstructive Surgery:

One of the mainstays of plastic and reconstructive procedures is toensure the patency and viability of grafting procedures. Hence, it isimportant to monitor and visualize the blood flow in diseased andreconstructed or grafted tissue, as well as their interface. Thegrafting procedures of interest involve those such as free tissuetransfer procedures, which transfer skin, vessels, muscle, and bone fromone part of the body to another. This procedure can be used, forexample, after treating cancer or removing a tumor or after an accidentor burn. The critical portion of a tissue transfer procedure isconnecting the removed vessels to the vessels in the receiving site.Likewise, monitoring the patency and viability of an anastomosis ofblood vessels is critical to the success of organ transplant orreplantation procedures (e.g., a finger or other body part). The subjectinvention can be embodied to provide real-time or near-real-time bloodflow information that assists surgeons in determining that thetransferred vessels have proper blood flow and connection.

Ophthalmic Surgery:

Ophthalmic surgeries are often precise and increasingly conducted withrobotic systems. For example, a number of surgeries (e.g., treatment ofDR and ROP) involve irradiation of the retina with intense beams oflaser to cauterize the vessels in the region to restrict undesiredvascular proliferation. Such a laser systems could be augmented withspeckle-based imaging systems that use a low-intensity laser in theinvisible spectrum and generate blood flow information in the ROI. Suchinformation might help the surgical system avoid certain vessels (e.g.,major vessels) and confirm that flow in the vessels of interest is asdesired (i.e., uninterrupted or stopped, as appropriate). The subjectinvention can be embodied to obtain and display real-time ornear-real-time blood flow information to facilitate operating ophthalmicsurgeons or surgical systems for decision making on navigation andoutcomes.

Cardiac Surgery:

Many cardiac surgeries, including coronary artery bypass grafting,angioplasty, or endarterectomies require intraoperative evaluation ofblood flow to ensure successful completion of the procedure. In suchprocedures, visual inspection with use of surgical loupes is a typicalmeans of evaluating vessel patency. The subject invention can beembodied to provide real-time or near-real-time visualization ofanatomical and physiological information in the FOV of the surgicalloupes.

Endoscopic Surgery:

Endoscopic surgeries typically involve manipulation or resection ofvessels, tissue, and organs. As with other surgical procedures, theability to identify the vessel anatomy and physiology in the surgicalsite is critical for navigation to prevent unintended injury or ruptureof the vessels and to identify areas of disease. For example, mesentericischemia (where blood flow to the gastrointestinal system is decreaseddue to blood vessel blockage), intraoperative, real-time ornear-real-time monitoring of blood flow in the intestinal tissue canfacilitate identification of specific regions of decreased flow toimprove, for example, the efficiency of plaque removal procedures or tominimize the portion of damaged tissue that must be removed. Likewise,the ability to evaluate the patency and viability of vessels and organsfollowing a resection is critical to the patient's outcome. In somecases these procedures are performed manually, semi-automatically, orautomatically using a computer-aided surgical system. The subjectinvention can be embodied to provide real-time or near-real-timevisualization of anatomical and physiological information during anendoscopic surgical procedure through the integration of LSCI withendoscopic instruments, with or without computer-aided surgicalequipment.

In some embodiments, the system is designed as a standalone device forobserving the target tissue in the surgical site. In some embodiments,the system is designed to operate in a modular fashion with a surgicalmicroscope for observing the target tissue in the surgical site. In someembodiments, the system is designed to operate in conjunction withexisting medical equipment, including electronic medical records; PACS,MRI, CT, and other imaging devices, laser ablation or electrocauterydevices; or computer-aided surgical systems. In various embodiments, thesystem is designed to display the real-time or near-real-time blood flowimages and other anatomical and physiological information in theviewfinder of a surgical microscope for observation by the surgeonduring the surgical procedure. In some embodiments, the system isdesigned to display the real-time or near-real-time blood flow imagesand other anatomical and physiological information on a monitor in thesurgical suite for observation by the surgeon and other members of thesurgical team during the surgical procedure. In some embodiments, thedisplay of the real-time or near-real-time blood flow images and otheranatomical and physiological information is designed to overlay onanother image (e.g., MRI or CT image of the preoperative anatomy, visuallight image, or ICG angiogram) of the surgical site FOV. In someembodiments, the display is designed to present the real-time ornear-real-time blood flow images and other anatomical and physiologicalinformation in one or more eyepieces of a surgical microscope.

In some embodiments, the system and method are designed for real-time ornear-real-time blood flow imaging during non-surgical medical proceduresto support clinical diagnosis or treatment decisions or for researchpurposes. In some embodiments, the system is designed to facilitateevaluation of physiological response to various stimuli, includingvisual stimuli, auditory stimuli, somatosensory stimuli, or motorstimuli. In some embodiments, the system is designed to facilitateevaluation of physical activity, including exercise, Valsalva maneuver,or physical therapy. In some embodiments, the system is designed tofacilitate evaluation of pharmacological or other therapeutic agents ordevices. In some embodiments, the system is designed for portable use ina clinical or community health environment.

In some embodiments, the system and method are designed for preclinicalresearch in animal models or for veterinary applications. The subjectinvention can be embodied appropriately to meet the size andflow-related technical requirements of the specific animal tissue thatis being imaged. For example, for imaging the rat brain, a FOV of 5 mm×5mm may be adequate, and vessels of interest are likely to have diametersthat are in the sub-millimeter range. Blood velocities and flow valuesare also different than in human vessels and, hence, the camera exposuretime that is used for image acquisition may be different than in theclinical-grade system. In some embodiments for animal use, the workingdistance of the system's objective lens to the point of focus of theoptical system may be shorter than in systems designed for clinicalsurgery. For example, in small animal research the exposed tissue isexpected to be relatively shallow and, hence, the working distance ofthe system's objective lens to the point of focus of the optical systemcan be less than 60 mm and be variable to accommodate for the opticalmagnification of the system that may be desired for specificapplications. Along with the relatively shorter working distance, themagnification and optical resolution for some embodiments for smallanimal use are higher. Application-specific requirements such as thediameter of the smallest vessel of interest in the target tissue, andthe field of view of the target tissue may determine the opticalmagnification and the pixel resolution of the camera used. Variousattributes of the system such as optical magnification, pixel size ofthe camera, size of the pixel array on the camera sensor, should bechosen such that the diameter of the smallest vessel of interest spansat least five pixels, and simultaneously, the active pixel area of thecamera sensor images the entire field of view desired.

In some embodiments for animal use, the system is designed to emphasizemodularity. In such embodiments, the system may comprise a stand to holdthe various elements (e.g., illumination and camera modules) and allowfor multiple degrees of freedom adjustment of the orientation tofacilitate imaging of the ROI through various access-based orapplication-specific constraints of the preparation. In someembodiments, the system may comprise one or more mechanisms (e.g., aspecialized platform or stereotaxic stand) for fixing, positioning, orsecuring the animal with respect to the system. In some embodiments,such mechanisms may be adjustable or modular for use in animals ofdifferent types and sizes. In some embodiments, the optical arrangementof the system can be adjusted to account for different applications andto accommodate various sizes of animals.

In various embodiments, the system and method are designed to compensatefor motion artifact. Acquisition of multiple image frames makes LSCIsusceptible to any motion artifacts. In such embodiments, the system isdesigned to reduce motion artifact by incorporating a stable surgicalmicroscope or animal stand and rapid acquisition (less than 40 ms) of asmall number of images (i.e., only 5 fast-acquired image frames instLSCI) for every blood flow image generated. In some embodiments, thesystem comprises one or more motion compensation mechanisms (e.g.,3-axis accelerometer) to detect large or fast motion and a mechanism andmethod to tag any resulting speckle data as potentially inaccurate. Insuch embodiments, the system may comprise a mechanism to indicate to theuser that the data is inaccurate, including through blanking of thedisplay until the undesired motion ceases or the display of anappropriate message in the FOV. In some embodiments, the system employsa threshold for pixel intensity to eliminate noise from the displayedblood flow image.

In some embodiments, the one or more motion compensation mechanisms usesone or more or a combination of accelerometer and image data. In suchembodiments, the system and method may involve the steps of andmechanism for feature detection (e.g., vessel detection using its ridgelike appearance), followed by estimation of image registrationparameters using an affine model with sub-pixel resolution. In someembodiments, accelerometer data may be used to bias the extraction ofregistration parameters through improved initialization of the motioncompensation mechanism. For example, the registration parameters may beused to register sequentially acquired image frames to the first frameprior to the calculation of laser speckle contrast. In some embodiments,the system comprises a processor with sufficient speed and a storagemodule with sufficient memory to facilitate the computationallyintensive process of real-time motion compensation (e.g., with real-timevideo mode, real-time vessel mode, or real-time relative mode). In someembodiments, the system is designed to facilitate motion compensation byacquiring image data in a snapshot mode. In some embodiments, afiduciary marker may be added to the imaging target to serve as thefeature for detection, motion identification, and compensation.

In some embodiments, the one or more motion compensation mechanisms usesinformation from other sensors (e.g., heart rate monitor, fingerplethysmograph, respirator, or other surgical, anesthesiological, ormedical equipment) to detect, calculate, or estimate motion artifact orto determine when and whether to indicate to the user that the data isinaccurate. In such embodiments, the system and method may involve thesteps of and mechanism for feature detection from the informationobtained from the other source (e.g., the peak or trough of a fingerplethysmogram, which correspond to systole and diastole of a cardiaccycle, or the peak or trough of a respirator, which correspond tocompletion of inspiration and expiration, respectively), followed byestimation of image registration parameters or a decision regarding theneed to inform the user of the potential inaccuracy of the data.

In some embodiments, the system and method are designed to compensatefor glare and stray reflections.

The target tissue and surrounding surgical site may have exposedfeatures that reflect light into the imaging optics towards the cameramodule, creating light artifacts (i.e., glare or stray reflections).Hence, in some embodiments, the system may comprise one or moremechanisms to detect such light artifacts and one or more mechanisms toindicate this potential inaccuracy to the user or compensate for thispotential inaccuracy. One embodiment of a mechanism to detect the lightartifact comprises an image-processing algorithm that identifies acluster of saturating pixels that remains approximately constant throughthe sequentially acquired image frames. One embodiment of a mechanism tocompensate for the potential inaccuracy due to the light artifactcomprises selectively blanking out those pixels that are gatheringerroneous data and displaying only those pixels that are gathering datawithout being affected by stray light.

In some embodiments, the system and method are designed to instruct tofollow one or more steps to rectify the cause of motion artifact orstray light. For example, the user may be asked to change the relativeposition between the system and the imaging target or stabilize theimage target and system with respect to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of a system forrapid examination of particulate flow in a target tissue.

FIGS. 2A, 2B, and 2C illustrate different embodiments of a systemdesigned for real-time estimation and visualization of blood flow duringsurgery.

FIGS. 3A and 3B illustrate two embodiments of a system for real-time ornear-real-time imaging of retinal blood flow.

FIG. 4 illustrates an embodiment of a system for imaging in anesthetizedand restrained animals.

FIG. 5 is a flowchart depicting an embodiment of a method for rapidexamination of particulate flow using LSCI.

FIG. 6 illustrates an embodiment of a spatiotemporal method ofcalculating laser speckle contrast for rapid examination of particulateflow in a target tissue.

FIG. 7 illustrates a method for performing LSCI on a field programmablegate array.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of the present subject matter refersto the accompanying drawings that show, by way of illustration, specificaspects and embodiments in which the present subject matter may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the present subject matter.The invention can assume various embodiments that are suitable to itsspecific applications.

FIG. 1 is a block diagram illustrating an embodiment of a system 100 forrapid examination of particulate flow in a target tissue 101. In variousembodiments, the target tissue 101 comprises any tissue, organ, or organsystem of any human or animal biological system, including but notlimited to the cornea, sclera, retina, epidermis, dermis, hypodermis,skeletal muscle, smooth muscle, cardiac muscle, brain tissue, the spinalcord, the stomach, large and small intestines, pancreas, liver,gallbladder, kidneys, endocrine tissue, and associated or disassociatedblood vessels and lymph vessels. In various embodiments, the system 100comprises at least one illumination module 110 that is configured togenerate at least one type of coherent light and to direct the generatedlight to the target tissue 101 being imaged; at least one illuminationoptics 120 that is configured such that the desired ROI is illuminatedwith the at least one type of coherent light; at least one camera module130 that is configured to capture light that is reflected or scatteredby the target tissue 101 being imaged; at least one imaging optics 140that is configured such that the desired ROI is focused on the camerasensor within the camera module 130 with desired specifications ofmagnification, field of view, speckle size, spot size; at least oneprocessor module 150 configured at least to estimate anatomical andphysiological information in real-time or near-real-time using the dataacquired by the camera module 130 and to control the operation of thesystem 100; at least one display module 160 configured to present theestimated anatomical and physiological information or equivalentparameters calculated from the image data by the processor module 150 orthe raw data acquired by the camera module 130; at least one storagemodule 170 configured to store the estimated anatomical andphysiological information or equivalent parameters calculated from theimage data by the processor module 150 or the raw data acquired by thecamera module 130 for temporary or future use; and at least one userinterface module 180 configured to allow the user or operator tointeract with the system 100 and program various options for featuresand parameters relevant to the performance of the various modules 110,120, 130, 140, 150, 160, 170, 180 of the system 100.

The illumination module 110 comprises one or more light sources suchthat at least one of the sources produces coherent light (e.g., a laser)for speckle production and LSCI. In some embodiments, the illuminationmodule 110 comprises additional light sources that produce coherent,non-coherent, or partially coherent light. The wavelength of the one ormore lights being emitted by the light sources in the preferredembodiment lies in the 100-micron to 2000-micron range. In someembodiments, one or more wide-band light sources is used to producelight with more than one wavelength. In some embodiments, the one ormore wide-band light sources is fitted with one or more filters tonarrow the band for specific applications. Typically, non-coherent lightsources are useful for reflectance- or absorption-based photography. Insome embodiments, direct visualization and focusing of the system 100 onthe target tissue 101 is achieved under non-coherent illumination. Insome embodiments, the illumination module 110 incorporates mechanisms tocontrol one or more of the power, intensity, irradiance, timing, orduration of illumination. Such a control mechanism may be electronic(examples include a timing circuit, an on/off switching circuit, avariable resistance circuit for dimming the intensity, or acapacitor-based circuit to provide a flash of light) or mechanical whereone or more optical elements (examples include an aperture, a shutter, afilter, or the source itself) may be moved in or out of the path ofillumination. In various embodiments, the light sources included in theillumination module 110 may be pulsatile or continuous, polarized ornon-polarized.

The illumination optics 120 comprise an arrangement of one or more lightmanipulation components, which includes but is not limited to lenses,mirrors, apertures, filters, beam splitters, beam shapers, polarizers,wave retarders, and fiber optics, that serve the purpose of deliveringlight from the illumination module 110 to the desired ROI in the targettissue 101. The illumination optics 120 for the various embodimentsincludes components that manipulate the light in a manner than is usefulfor imaging the tissue of interest based on the specific application. Insome embodiments, the illumination optics 120 includes a polarizer inthe path of illumination that polarizes the light in a manner thatsignificantly attenuates the light except when reflected or scattered bythe target tissue 101.

The camera module 130 comprises at least one camera sensor or imageacquisition device that is capable of transducing incident light to adigital representation (called image data). The camera module 130 isconfigured to direct the image data for further processing, display, orstorage. In some embodiments, the camera module 130 comprises mechanismsthat control image acquisition parameters, including exposure time(i.e., time for which the camera sensor pixel integrates photons priorto a readout), pixel sensitivity (i.e., gain of each pixel), binning(i.e., reading multiple pixels as if it was one compound pixel), activearea (i.e., when the entire pixel array is not read out), among others.In the various embodiments, the at least one camera sensor used in thecamera module 130 is a charge coupled device (CCD), complementary metaloxide semiconductor (CMOS), metal oxide semiconductor (MOS), based onphoto-tubes, or another similar technology designed to capture imagedata.

The imaging optics 140 comprise an arrangement of one of more lightmanipulation components that serve the purpose of focusing the ROI ofthe target tissue 101 on to the at least one camera sensor of the cameramodule 130. In some embodiments, the imaging optics 140 comprise a meansto form more than one image of ROI or sub-regions of the ROI of thetarget tissue 101. In some embodiments, the more than one image projectsonto the one or more camera sensors or on the observer's retina throughan eyepiece. In the various embodiments, the imaging optics 140determine the imaging magnification, the field of view (FOV), size ofthe speckle (approximated by the diameter of the Airy disc pattern), andspot size at various locations within the FOV. In some embodiments, theimaging optics 140 includes light manipulation components that, inconjunction with components of the illumination optics 120, reduce theundesired glare resulting from various optical surfaces.

The processor module 150 comprises one or more processing elementsconfigured to calculate, estimate, or determine, in real-time ornear-real-time, one or more anatomical and physiological information orequivalent parameters calculated from the image data. The processormodule 150 further comprises one or more processing elements configuredto implement control functions for the system 100, including control ofoperation and configuration parameters of the camera module 130 (e.g.,exposure time, gain, acquisition timing) and the illumination module 110(e.g., timing, duration, and synchrony of illumination); control of thetransmission of image data or derivatives thereof to the display module160 or the storage module 170; control of which anatomical andphysiological information or equivalent parameters should be calculated,estimated, or determined by the processor module 150; control of theposition and orientation of one or more components of the illuminationmodule 110, illumination optics 120, camera module 130, or imagingoptics 140; and control of the power, safety criteria, operationalprocedures of the system 100.

In various embodiments, the processor module 150 is configured tocalculate, estimate, or determine one or more anatomical andphysiological information or equivalent parameters calculated from theimage data in one or more of the following modes:

-   -   Real-time video mode—In the real-time video mode, the processor        module 150 is configured to calculate, estimate, or determine        one or more anatomical and physiological information or        equivalent parameters calculated from the image data based on        certain predetermined set of parameters and in synchrony or        near-synchrony with the image acquisition. In the real-time        video mode, the frame rate of the video presented by the display        module 160 is greater than 16 frames per second (fps), allowing        the surgeon to perceive uninterrupted video (based on the        persistence of vision being 1/16^(th) of a second).    -   Real-time vessel mode—In real-time vessel mode, the system 100        is configured to allow the surgeon to select, using automatic or        semi-automatic means, one or more vessels and to emphasize the        anatomical and physiological information in the selected vessels        over other vessels in the FOV. In some embodiments, the system        100 is configured to allow the surgeon to select all arteries or        all veins, extracted automatically, in the entire FOV or an ROI        of the FOV. In such embodiments, the extraction may be achieved        by either (a) computing the anatomical or physiological        information in the entire field but displaying only the        anatomical or physiological information in the selected vessels,        or (b) computing the anatomical or physiological information        only in the selected vessels and displaying the anatomical or        physiological information accordingly, or (c) computing the        anatomical or physiological information in the entire field and        enhancing the display of the selected vessels through an        alternate color scheme or by highlighting the pre-selected        vessels centerlines or edges.    -   Real-time relative mode—In the real-time relative mode, the        processor module 150 includes the baseline values of anatomical        and physiological information in its computation of        instantaneous values of anatomical or physiological information.        The real-time relative mode may be implemented as a difference        of instantaneous values of anatomical or physiological        information from the baseline values, or as a ratio of the        anatomical or physiological information with respect to baseline        values.    -   Snapshot mode—In the snapshot mode, the processor module 150        generates a single image of the anatomical or physiological        information in the surgical FOV. In this embodiment, the        processor module 150 may utilize a greater number of frames for        computing the anatomical or physiological information than it        utilizes during the real-time modes, since the temporal        constraints are somewhat relaxed. In the snapshot mode, all the        functionalities of the real-time modes are also possible (e.g.,        display of change of blood flow instead of blood flow, or        enhanced display of a set of selected vessels).

The display module 160 comprises one or more display screens configuredto present the estimated anatomical and physiological information orequivalent parameters calculated from the image data by the processormodule 150 or the raw data acquired by the camera module 130. In someembodiments, the one or more display screens are physically located inclose proximity to the remaining elements of the system 100. In someembodiments, the one or more display screens are physically locatedremotely from the remaining elements of the system 100. In the variousembodiments, the one or more display screens are connected by wired orwireless means to the processor module 150. In some embodiments, thedisplay module 160 is configured to provide the observer with avisualization of the ROI and the estimated anatomical and physiologicalinformation or equivalent parameters calculated from the image data bythe processor module 150. In the various embodiments, the display module160 is configured for real-time visualization, near-real-timevisualization, or retrospective visualization of imaged data orestimated anatomical and physiological information or equivalentparameters calculated from the image data that is stored in the storagemodule 170. Various aspects of anatomical and physiological information,or equivalent parameters and other outputs of the processor may bepresented in the form of monochrome, color, or pseudo-color images,videos, graphs, plots, or alphanumeric values.

The storage module 170 comprises one or more mechanisms for archivingelectronic data, including the estimated anatomical and physiologicalinformation or equivalent parameters calculated from the image data bythe processor module 150 or the raw data acquired by the camera module130. In various embodiments, the storage module 170 is configured tostore data for temporary and long-term use. In various embodiments, theone or more mechanisms includes random access memory (RAM) units,flash-based memory units, magnetic disks, optical media, flash disks,memory cards, or external server or system of servers (e.g., acloud-based system) that may be accessed through wired or wirelessmeans. The storage module 170 can be configured to store data based on avariety of user options, including storing all or part of the estimatedanatomical and physiological information or equivalent parameterscalculated from the image data by the processor module 150 or the rawdata acquired by the camera module 130.

The user interface module 180 comprises one or more user inputmechanisms to permit the user to control the operation and preferredsettings of the various modules 110, 120, 130, 140, 150, 160, 170, 180of the system 100. In various embodiments, the one or more user inputmodule includes a touch-screen, keyboard, mouse or an equivalentnavigation and selection device, and virtual or electronic switchescontrolled by hand, foot, eye, or voice. In some embodiments, the one ormore user input mechanisms is the same as the one or more displayscreens of the display module 160.

In some embodiments, the user interface module 180 is customized for twotypes of users. The primary user of the system 100 is one or moresurgeons performing the surgery. In some embodiments, the system 100 isconfigured to facilitate performing the surgery via computer-aidedsurgical systems. The anatomical and physiological information providedto the one or more surgeons to assist with decision-making during thesurgical operation at various times. The user interface module 180 ofthe system 100 allows the user to:

-   -   Turn on/off (or standby) the visualization of anatomical or        physiological from surgical microscope FOV as desired (referred        to as the “real-time video mode”), which is achievable using a        variety of triggers, including the pressing of a physical or        virtual button or similar switch by the surgeon's hand, finger        or foot, the creation of an audible trigger, or the motion of an        object or body part;    -   Acquire and visualize accurate and real-time anatomical or        physiological information in a blood vessel of interest        (referred to as the “real-time vessel mode”), which is        implemented by the system 100 either on a continuous basis, or        when triggered by the surgeon using a variety of triggers,        including the pressing of a physical or virtual button or        similar switch by the surgeon's hand, finger or foot, the        creation of an audible trigger, or the motion of an object or        body part;    -   Visualize either the instantaneous estimation of anatomical or        physiological information or the change in measurement of        anatomical or physiological information (referred to as the        “real-time relative mode”) from a preset baseline value, which        are both implemented by the system 100 through appropriately        storing baseline values in the storage module 170 and        configuring the processor module 150 to either not utilize or        utilize the baseline values in its computation of instantaneous        values of the anatomical or physiological information to obtain        the anatomical or physiological information or change in the        anatomical or physiological information.    -   Store snapshots or videos of the anatomical or physiological        information in the surgical field if needed (referred to as the        “snapshot mode”), which is implemented by the system 100 by        providing the user a “capture” button (physical or virtual), and        subsequently handled by the processor module 150, which directs        the data to the storage module 170.

The secondary user of the system is the assisting staff of theoperation, potentially including scrub nurse, assisting nursepractitioner, anesthesiologist, and other clinicians in the operatingroom or positioned remotely outside the operating room during theoperation. The user interface module 180 of the system 100 allows thesecondary user to assist the surgeon to set up the system, modifyparameters, and perform certain functions in real-time that the primaryuser may require (capture image, save video, etc.), some or all of whichmay be enabled by a portion of the user interface module 180 that iscustomized for secondary access. Thus, in some embodiments, the userinterface module 180 comprises two sub-modules, a first sub-module thatwill be accessible to the operating surgeon and a second sub-module thatwill be accessible by the secondary user.

FIGS. 2A, 2B, and 2C illustrate different embodiments of a systemdesigned for real-time estimation and visualization of blood flow duringsurgery. The embodiment in FIG. 2A shows a system 200 that includes aphysically-integrated surgical microscope 201. The illumination opticsand imaging optics leverage the optical assembly 205 of the surgicalmicroscope 201. The system 200 estimates blood flow within an FOV 210the size of which is determined by the magnification settings of thesurgical microscope 201. The system 200 estimates the blood flow withinthe depth of focus as set by the surgical microscope 201. When used inhuman surgical environments, the FOV 210 has a diameter that ranges fromapproximately 10 mm to 50 mm in diameter. When used in veterinaryenvironments, the FOV 210 has a diameter that ranges from approximately5 mm to 50 mm in diameter.

In FIG. 2A, the system 200 utilizes multiple optical ports 206 toengage 1) the imaging optics 203 to form an image of the FOV 210 on thecamera sensor of the camera module 204, and 2) the display module 207 toproject the anatomical and physiological information in one or more ofthe eyepieces 208 of the surgical microscope 201. In some embodiments,an aperture is included in the imaging optics 203 that determines thediameter of the Airy disc (i.e., speckle size) for a given magnificationand the wavelength of the laser used. The system 200 employs anillumination module 202 with laser diode of light in the invisible range(700 nm to 1000 nm) to prevent disruption of the surgical field, auniform beam shaper to achieve uniform top-hat or flat-top illuminationthat transforms a Gaussian beam of the laser diode into a uniformintensity distribution, and a near-infrared (NIR) polarizer to generatea linearly polarized illumination. In some embodiments, laser diodehomogenization and reshaping may be assisted by two orthogonal Powelllenses. In some embodiments, one or more fiber-optic illumination portsmay be employed to transmit light to the surgical area to illuminate theROI 211. In some embodiments, the wavelength of coherent light isselectively matched to fluorescent dyes to combine LSCI with otherimaging techniques (e.g., ICG angiography).

The camera module 204 includes a CMOS camera sensor that comprises a2048×2048 pixel array, each of which is 5.5 μm×5.5 μm in size such thatthe imaging optics 203 forms an image of the entire FOV 210 on thecamera sensor of the camera module 204. In various embodiments, thepixels of the camera sensor may be binned at the hardware level orsoftware level such that the data is read out in a manner that eachframe contains 1024×1024, 512×512, or 256×256 pixel array (correspondingto 2×2, 4×4, or 8×8 binning, respectively). In some embodiments, dataacquired by the camera module 204 is directed to an FPGA 209 via acamera link at a rate greater than or equal to 120 frames per second. Insome embodiments, the FPGA performs stLSCI calculations and generates24-bit RGB color representations of blood flow information forpresentation to the user via the display module 207 over an HDMIinterface.

FIG. 2B shows an illustration of a system 220 designed for use withsurgical or dental loupes. The system 220 comprises an illuminationmodule 221 that is configured to generate coherent light in theinvisible range (700 nm to 1000 nm) and non-coherent light in thevisible range (400 nm to 700 nm) directed to the target tissue beingimaged; illumination optics 222 that is configured such that the desiredROI is illuminated with the coherent light and illumination optics 223that is configured such that the desired ROI is illuminated with thenon-coherent light; a camera module 224 that is configured to capturelight that is reflected or scattered by the target tissue being imaged;imaging optics 225 that is configured such that the desired ROI isfocused on the camera sensor within the camera module 224 with desiredspecifications of magnification, field of view, speckle size, spot size;a cable 226 for facilitating data transmission between the camera module224, the illumination module 221, and the processor module 227, which isconfigured to estimate anatomical and physiological information inreal-time or near-real-time using the data acquired by the camera module224 and to control the operation of the system 220; two display modules228 and 229 configured to present the estimated anatomical andphysiological information or equivalent parameters calculated from theimage data by the processor module 227 or the raw data acquired by thecamera module 224; a storage module 230 configured to store theestimated anatomical and physiological information or equivalentparameters calculated from the image data by the processor module 227 orthe raw data acquired by the camera module 224 for future use; and auser interface module 231 configured to allow the user or operator tointeract with the system 220 and program various options for featuresand parameters relevant to the performance of the various modules 221,222, 223, 224, 225, 226, 227, 228, 229, 230 of the system 220.

FIG. 2C shows an illustration of a system 240 designed for use in anendoscopic surgical setting. The system 240 comprises an illuminationmodule 241 that is configured to generate coherent light in theinvisible range (700 nm to 1000 nm) and non-coherent light in thevisible range (400 nm to 700 nm) directed to the target tissue beingimaged; illumination optics 242 that employs one or more fiber opticssuch that the desired ROI is illuminated with the coherent light andnon-coherent light; a camera module 243 that is configured to capturelight that is reflected or scattered by the target tissue being imaged;imaging optics 244 that is configured such that the desired ROI isfocused on the camera sensor within the camera module 243 with desiredspecifications of magnification, field of view, speckle size, spot size;a processor module 245 that is configured to estimate anatomical andphysiological information in real-time or near-real-time using the dataacquired by the camera module 243 and to control the operation of thesystem 240; a display module 246 configured to present the estimatedanatomical and physiological information or equivalent parameterscalculated from the image data by the processor module 245 or the rawdata acquired by the camera module 243; a storage module 247 configuredto store the estimated anatomical and physiological information orequivalent parameters calculated from the image data by the processormodule 245 or the raw data acquired by the camera module 243 for futureuse; and a user interface module 248 configured to allow the user oroperator to interact with the system 240 and program various options forfeatures and parameters relevant to the performance of the variousmodules 241, 242, 243, 244, 245, 246, 247 of the system 240. The system240 comprises a handle 249 to facilitate handheld use during surgery.

FIGS. 3A and 3B illustrate two embodiments of a system for real-time ornear-real-time imaging of retinal blood flow. In the embodimentillustrated in FIG. 3A, the system 300 is designed for clinical use forresearch or diagnostic purposes. The system 300 comprises a retinalimaging device 301 that houses an illumination module configured togenerate coherent light in the visible or invisible range (400 nm to1500 nm) and non-coherent light in the visible range (400 nm to 700 nm)directed to the desired ROI of the retina; illumination optics that isconfigured such that the desired ROI of the retina is illuminated withthe coherent light and non-coherent light; a camera module that isconfigured to capture light that is reflected or scattered by theilluminated ROI of the retina; imaging optics that is configured suchthat the desired ROI of the retina is focused on the camera sensorwithin the camera module with desired specifications of magnification,field of view, speckle size, spot size. The retinal imaging device 301is designed to fit onto a bench-top stand 302 that allows the user tomanipulate the position and orientation (i.e., height, angle, andproximity) of the device to the retina of the subject 303 being imaged.A chin rest 304 is used to reduce motion of the subject's 303 head andto fix the relative distance between the subject's 303 retina and theretinal imaging device 301. The system 300 further comprises a laptopcomputer 305 that houses a processor module configured to estimateanatomical and physiological information in real-time or near-real-timeusing the data acquired by the camera module and to control theoperation of the retinal imaging device 301; a display module configuredto present the estimated anatomical and physiological information orequivalent parameters calculated from the image data by the processormodule or the raw data acquired by the camera module of the retinalimaging device 301; a storage module configured to store the estimatedanatomical and physiological information or equivalent parameterscalculated from the image data by the processor module or the raw dataacquired by the camera module for future use; and a user interfacemodule configured to allow the user or operator to interact with theretinal imaging device 300 and program various options for features andparameters relevant to the performance of the various modules of thesystem 300. The retinal imaging device further comprises a displaymodule 306 configured to present the estimated anatomical andphysiological information or equivalent parameters calculated from theimage data by the processor module or the raw data acquired by thecamera module.

In FIG. 3B, the system 320 is implemented as a retinal imaging device321 designed for handheld use. The retinal imaging device 321 houses anillumination module comprising of a diode laser (e.g., a 650 nm redlaser) and a visible wavelength LED source (e.g., an LED with peakemission wavelength of 540 nm); a camera module comprising of a CMOScamera; display module 322 comprising of an LCD screen; a storage modulecomprising of an SD card module; a processor module comprising of anArduino-based microcontroller or an FPGA. The user interface module isimplemented through a combination of switches on the device or on aremote controller, one or more on-screen menus on the display module322, and a keyboard and mouse for parameter and information entry. Theretinal imaging device 321 employs a rubber eye cup 323 to stabilize thedevice with respect to the eye of the subject 324. In some embodiments,the retinal imaging device 321 includes a wireless module thatfacilitates transmission of electronic data to a local laptop computeror mobile computing device or to a remote server or server system. Insome embodiments, the system 320 employs a laptop computer or mobilecomputing device as a secondary display module. In some embodiments, thesystem 320 includes a transmission module that facilitates transmissionof electronic data to a remote server or server system for furtherstorage, processing, or display. In some embodiments, the system 320comprises a processing module configured to display anatomical andphysiological information from retinal vasculature with a latency ofless of than 100 milliseconds.

FIG. 4 illustrates an embodiment of a system for imaging in anesthetizedand restrained animals. The system 400 comprises an imaging device 401that houses an illumination module configured to generate at least onecoherent light in the visible or invisible range (400 nm to 1500 nm) andat least one non-coherent light in the visible range (400 nm to 700 nm)directed to the target tissue of an anesthetized and restrained animal402; illumination optics that is configured such that the target tissueis illuminated with the coherent light and non-coherent light; a cameramodule that is configured to capture light that is reflected orscattered by the illuminated ROI of the target tissue; imaging opticsthat is configured such that the desired ROI of the target tissue isfocused on the camera sensor within the camera module with desiredspecifications of magnification, field of view, speckle size, spot size.The imaging device 401 is designed to fit onto a bench-top stand 403that allows the user to manipulate the position and orientation (i.e.,height, angle, and proximity) of the device relative to the animal 402being imaged. The system further comprises a platform 404 (e.g., astereotaxic frame) used to reduce motion of target tissue of the animal402 and to fix the relative distance between the target tissue of theanimal 402 and the imaging device 401. The system 400 further comprisesa laptop computer 405 that houses a processor module configured toestimate anatomical and physiological information in real-time ornear-real-time using the data acquired by the camera module and tocontrol the operation of the imaging device 401; a display moduleconfigured to present the estimated anatomical and physiologicalinformation or equivalent parameters calculated from the image data bythe processor module or the raw data acquired by the camera module ofthe imaging device 401; a storage module configured to store theestimated anatomical and physiological information or equivalentparameters calculated from the image data by the processor module or theraw data acquired by the camera module for future use; and a userinterface module configured to allow the user or operator to interactwith the imaging device 401 and program various options for features andparameters relevant to the performance of the various modules of thesystem 400. In some embodiments, the system 400 includes a transmissionmodule that facilitates transmission of electronic data to a remoteserver or server system for further storage, processing, or display. Insome embodiments, the imaging device 401 is designed specifically forimaging of surface or subcutaneous vasculature. In some embodiments, theimaging device 401 is designed specifically for imaging of thevasculature of surgically exposed tissue. In some embodiments, theimaging device 401 is designed specifically for imaging of retinalvasculature. In some embodiments, specific parts (e.g., opticalelements) of the imaging device 401 may be exchanged with other parts tooptimize the system 400 for imaging the vasculature of specific tissue.

FIG. 5 is a flowchart depicting an embodiment of a method for rapidexamination of particulate flow using LSCI. In this embodiment, the LSCIprocess 500 for rapid examination of particulate flow begins oncetriggered 501. In various embodiments, the trigger 501 that starts theLSCI process 500 can be manual (i.e., user-generated), automated (i.e.,system-generated), or semi-automated (i.e., user- or system-generated).Once the triggering step 501 has commenced, the system that implementsthe LSCI process 500 obtains the necessary parameters, includingexposure time, frame rate, resolution, binning factor, and gain. Thevarious parameters can be provided by either the user or obtained frommemory. Parameters may be modified manually or automatically usingfeedback from the imaging result and quality of one or more electronicdata. The system then, at 503, illuminates the ROI of the target tissuewith coherent light and acquires, at 504, a stack of N frames under thiscoherent light illumination at the predetermined exposure time and gain.Next, the system calculates, at 505, speckle contrast, K, for the pixelsof interest in the field of view, using the N frames of acquired speckleimage data, generating an LSCI image (Image Result 1) at 506. From theLSCI image the system estimates, at 507, blood velocity or flow,generating Image Result 2 at 508. At 509, the system converts ImageResult 2 to a pseudo-color representation of blood velocity or flow(Image Result 3), providing for intuitive visualization of bloodvelocity or flow information. The system displays, at 511, Image Result1, Image Result 2, or Image Result 3, as appropriate, depending on theuser-selected or preset display setting. Based on the parameter settingsat 502, the LSCI process 500 continues to provide rapid examination ofparticulate flow. An embodiment may generate Image Result 3 directlyfrom Image Result 1, at 512, using pre-determined lookup tables thatassign color-codes directly to speckle contrast values.

FIG. 6 illustrates an embodiment of a spatiotemporal method ofcalculating laser speckle contrast for rapid examination of particulateflow in a target tissue. The method 600 is intended to provide real-timeor near-real-time acquisition, processing, and display of blood flowinformation from the vasculature of any tissue. The method 600 beginswith the acquisition, at 601, of speckle image frames of the vasculatureunder coherent light illumination. In this embodiment, a stack of N=5speckle image frames are acquired at 601. In other embodiments, thestack of speckle image frames acquired at 601 ranges from 2 to 21(larger number of frames may be enabled by cameras with ultrafast imageacquisition). The stack of speckle image frames acquired at 601 aretransferred and processed at 602 using stLSCI to calculate the laserspeckle contrast values and generate an LSCI image at 603. The LSCIimage is processed at 604 to estimate the blood flow in the vasculaturewithin the FOV of the speckle image frames acquired at 601. In someembodiments, the flow estimation at 604 involves integration of bloodvelocities across the cross-section of the vessel to provide cumulativeflow in one or more vessels at one or more cross-sections; while in someembodiments, only blood velocity may be estimated and interpreted as thelocalized blood flow at the underlying pixel. Some embodiments mayimplement both methods of flow estimation, and permit the user to selecta desired method. The flow estimation at 604 generates a blood flowimage for visualization by a user or further processing. The method 600continuously repeats as additional speckle image frames are acquired at601. In various embodiments, the stack of speckle image frames acquiredat 601 used to generate each subsequent LSCI image at 603 and thecorresponding blood flow image at 605 includes 0 to N−1 of the speckleimage frames in the previous stack, where n is the number of speckleimage frames acquired at 601 to produce the LSCI image at 603 and thecorresponding blood flow image at 605. By rapid visualization of newblood flow images at 605, the method 600 is able to achieve a real-timeor near-real-time display of blood flow information from the vasculatureof the imaged tissue.

FIG. 7 illustrates a method for performing LSCI on a field programmablegate array. In this embodiment, the method 700 begins with theacquisition of a stack of speckle image frames, which are transferred at702 via an FPGA camera module interface at 701. The FPGA utilizes afinite number of memory and temporary registers to compute laser specklecontrast images according to the spatio-temporal processing scheme. Insome embodiments, the FPGA receives 1024×1024 pixel data and stores itinto the FPGA's Direct Memory (FPGADM) 703. The frames continue torefresh until the method 700 is halted. In this embodiment, at 704 thefirst 5 frames are copied from the FPGADM and stored in a differenttemporary location within the FPGADM. The processing on these 5 framesbegins at 705 and, in parallel, the next 5 frames arrive at the framerate of the camera and are similarly stored on the FPGADM at 703.Acquiring pixels at 82 MHz with four pixels per clock requires about 4ms to store a 1024×1024 frame, allowing 20 ms to complete all processingon the 5 frames before the next 5 frames are ready for processing.Starting from the bottom right corner, 25 pixels (equivalent to a 5×5pixel spatial window) at a time are read from each copied frame, paddingthe edge cases with zeros. The group of pixels are sent to two memorymodules per frame in parallel. The first memory module (M1), at 705,maintains a sum of the pixel values while the second memory module (M2),at 706, maintains a sum of the square of pixel values. Both the modulesat 705 and 706 store the sums of the first column of 5 pixels andsubtract it from the total for the next pixel in the current line,allowing the FPGA to read only 5 pixels for the rest of the outputs forthe current line instead of 25. The outputs of all the M1 modules areadded at 707 and then squared at 708 to form an output (Sum_Sq) whilethe outputs of all the M2 modules are summed at 707 to form an output(Sq_Sum). Next, Sq_Sum is shifted bitwise to the left by two and thensummed with Sq_Sum (equivalent to multiplying by 5) at 709. This resultis, at 710, divided by Sum_Sq and reduced by 1 to produce the final sumof the group of pixels across the 5 frames. At 711, the square root ofthis final sum produces the K value, at 712, for the pixel. The method700 repeats for each line in the frames and then for the next set offive frames. In some embodiments, where the 20 ms time requirementcannot be met, another set of modules is added that starts from the topright corner of the frame.

Once the K value is computed for a pixel, the value of l/τ_(c) isobtained for the pixel using look-up tables stored in the memory of theFPGA. This value of l/τ_(c) indicates the amount of perfusion at thepixel. Each values of l/τ_(c) has a unique representation in pseudocolor(in the red-green-blue of RGB space). Thus, each matrix of l/τ_(c)values is transformed using look-up tables to three matrices, one eachfor the red, green, and blue components of the pseudocolorrepresentation of the entire ROI. As described, the computation ofl/τ_(c) as an intermediate step may be unnecessary, and the RGB matricesmay be computed directly from the K values using look-up tables. Inaddition, the FPGA also adds a finite time-latency to the stream of rawimages acquired from the camera module, and creates a linear combinationof the raw image and each of the RGB matrices. When the latency ismatched with the amount of time required for the FPGA to generate thefirst set of RBG matrices measured from the onset of image acquisition,this processing scheme creates a stream of compound images wherein theblood flow information is depicted in pseudo-color and overlaid on theraw image of the target ROI. This stream of compound images that lag theinput by a specific latency constitute the output in this embodiment.

The FPGA then directs the output (values of l/τ_(c)) as a 24-bit RGBcolor representation to the display module. In this embodiment, thedisplay module comprises an LCD screen that displays the stream ofcompound images in real-time or near-real-time, as determined by thelatency introduced during the generation of the output image stream. TheLCD screen includes a driver module that parses the streaming image dataand displays it on an appropriately sized screen.

What is claimed is:
 1. A vascular imaging system, comprising: at least afirst light source configured to generate at least first coherent lightto illuminate a target tissue; an image acquisition device configured tocapture light that is reflected or scattered by the target tissue; afirst optical assembly configured to direct the first coherent light toa region of interest of the target tissue; a second optical assemblyconfigured to direct the reflected or scattered light from the region ofinterest of the target tissue to the image acquisition device; and oneor more processors configured to: calculate laser speckle contrastvalues at any pixel in any acquired image frame using data from the saidpixel and the said pixel's adjacent spatial and temporal neighborhoodcomprising one or more additional pixels in the same said any acquiredframe and corresponding pixels from a predetermined number of adjacentpreviously acquired frames, wherein data from said any acquired imageframe is also used to calculate second laser speckle contrast values forat least one subsequently acquired image frame.
 2. The vascular imagingsystem of claim 1, wherein the first coherent light has a wavelength inthe invisible infrared or near infrared spectrum.
 3. The vascularimaging system of claim 1, further comprising: a second light sourceconfigured to generate first non-coherent light to illuminate the targettissue.
 4. The vascular imaging system of claim 1, wherein the targettissue comprises one or more of a cornea, sclera, retina, epidermis,dermis, hypodermis, skeletal muscle, smooth muscle, cardiac muscle,cerebrovascular tissue, stomach, large or small intestines, pancreas,liver, gallbladder, kidneys, or lymphatic tissue of a human or animal.5. The vascular imaging system of claim 1, further comprising: a displaymodule configured to present electronic data generated by the one ormore processors; and one or more interface modules configured to allow auser to interact with the electronic data; wherein the electronic datacomprises image data captured by the image acquisition device,anatomical or physiological information calculated from the image data,and/or patient-specific data acquired from one or more other sourcesincluding one or more of electronic health records, electronic medicalrecords, personal health records, picture archiving and communicationssystems, heart rate monitor, finger plethysmograph, respirator, or othersurgical, anesthesiological, or medical equipment.
 6. The vascularimaging system of claim 5, wherein the vascular imaging system isfurther configured to perform angiography, wherein said angiographycomprises one or more of fluorescein angiography, indocyanine greenangiography, or angiography using an appropriate contrast agent or dye.7. The vascular imaging system of claim 1, further comprising: a displaymodule configured to present an overlaid visualization of electronicdata generated by the one or more processors on a view of the targettissue or directly on the target tissue.
 8. The vascular imaging systemof claim 1, wherein the one or more processors are configured tocompensate for motion artifact.
 9. The vascular imaging system of claim1, wherein the vascular imaging system is configured for performingreal-time or near real-time laser speckle contrast imaging duringsurgical procedures.
 10. The vascular imaging system of claim 1, whereinone or more components of the vascular imaging system are configured forportability, wherein said portability includes handheld, head-mounted,or other wearable use or integration into a movable trolley-type system.11. The vascular imaging system of claim 1, wherein one or morecomponents of the vascular imaging system are configured for endoscopicimaging.
 12. The vascular imaging system of claim 1, wherein one or morecomponents of the vascular imaging system are configured forintravascular imaging.
 13. The vascular imaging system of claim 1,wherein the vascular imaging system interacts with other sensory,therapeutic, or disease management systems to generate at least oneactionable output.
 14. The vascular imaging system of claim 1, wherein:the one or more processors are further configured to calculate one ormore of anatomical information or physiological information of a vessel;and the vessel is one or more of a naturally occurring or artificialblood vessel.
 15. The vascular imaging system of claim 14, wherein theartificial blood vessel includes a tube through which blood flows or canbe directed to flow.
 16. The vascular imaging system of claim 1, whereinthe one or more processors are configured to calculate a square of alaser speckle contrast value for a certain pixel in a certain imageframe by: calculating a sum of one or more pixel intensities that have apre-determined spatial or temporal relationship with said certain pixel;calculating a sum of squares of the one or more pixel intensities;maintaining a first memory location within which said calculated sum ofthe one or more pixel intensities is stored; maintaining a second memorylocation within which said calculated sum of squares of the one or morepixel intensities is stored; and calculating the square of the laserspeckle contrast value by subtracting one from the result of dividingthe product of a value in the second memory location and a number offrames from which the one or more pixel intensities are selected by asquare of the value in the first memory location.
 17. The vascularimaging system of claim 1, further comprising: at least a second lightsource configured to generate at least second coherent light having awavelength different than that of the first coherent light such that thefirst coherent light and the second coherent light penetrate the targettissue to different extents.
 18. The vascular imaging system of claim16, wherein: for any value of n between 1 and 100, the said one or morepixel intensities correspond to intensity of the said certain pixel in acertain image frame, intensities of a first plurality of pixelsspatially adjacent to the certain pixel in a certain image frame,intensity of n pixels each obtained from n frames temporally adjacent tothe certain image frame at a same spatial location as the certain pixelin a certain image frame, and intensities of n plurality of pixelsspatially adjacent to each of the said n pixels in their respective nadjacent frames.
 19. The vascular imaging system of claim 18, whereinthe one or more processors are configured to calculate the laser specklecontrast value for said certain pixel by determining a square root ofsaid square of laser speckle contrast value for said certain pixel. 20.The vascular imaging system of claim 18, wherein the one or moreprocessors are configured to determine an estimate of blood flow at saidcertain pixel by representing said square of laser speckle contrastvalue with another unique set of values.
 21. The vascular imaging systemof claim 20, wherein the said another unique set of values is one ormore of a single number, a percentage, or a set of numbers thatrepresent a color scheme.
 22. The vascular imaging system of claim 16,wherein one or more of a value in the first memory location, a value inthe second memory location, a calculated square of a laser specklecontrast value, or a calculated laser speckle contrast value are updatedwhen a new image frame is received by the processor from the imageacquisition device.
 23. The vascular imaging system of claim 22, whereinthe value in the first memory location is updated by subtracting the sumof pixel intensities from pixels in the oldest image frame to reside atthe first memory location and adding the sum of pixel intensities fromspatially corresponding pixels in said new image frame.
 24. The vascularimaging system of claim 22, wherein the value in the second memorylocation is updated by subtracting the sum of squares of pixelintensities from pixels in the oldest image frame to reside at the firstmemory location and adding the sum of squares of pixel intensities fromspatially corresponding pixels in said new image frame.
 25. The vascularimaging system of claim 20, wherein the unique set of values is updatedwhen a new image frame is received by the processor from the imageacquisition device.
 26. The vascular imaging system of claim 14,wherein: the anatomical information includes one or more of a diameter,tortuosity, depth in the target tissue, length, or type of the vessel;and the physiological information includes one or more of blood flow,blood velocity, change in blood flow, change in blood velocity, orspatial distribution of blood flow in the vessel.